Conventionally, there is known an apparatus which provides a visual stimulus to a driver using a LED mounted to a dashboard of a vehicle or a LED fixed (head-mounted) in front of the driver and which measures a driver's driving ability reduction based on a response result, which is a driver's button operation in response to the visual stimulus (see, for example, Non Patent Document 1).    Non Patent Document 1: Gary L. Rupp, Performance Metrics for Assessing Driver Distraction: The Quest for Improved Road Safety, SAE International